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Introductory Timer Lab

The TON Timer …. (Timer ON Delay)

– From the LogixPro Simulations Menu, select the I/O Simulation.
– Clear out any existing program by selecting the “New” entry within the File menu, and then select the “Clear Data Table” entry within the Simulations menu.
– Now enter the next program being careful to enter the addresses exactly as shown.
– Confirm that you have entered the number 100 as the timer’s preset value. This value represents a 10 second timing interval (10×0.1) as the timebase is fixed at 0.1 seconds:

– Once you have your program entered, and have ensured that it is correct, download it to the PLC.
– Make sure that Switch I:1/0 is Open, after which place the PLC into the Run mode.
– Right click on the Timer instruction, and select “GoTo DataTable” from the drop-down menu.
– Note the initial value of timer T4:1’s accumulator and preset in the spaces below. Also indicate the state of each of the timer’s control bits within the spaces provided:
Initial State (Switch I:1/0=Open):
T4:1.ACC = _____ T4:1.PRE = ______ T4:1/EN = ____ T4:1/TT = ____ T4:1/DN = ____

– Close switch I:1/0, and thoroughly observe the incrementing of the timer’s accumulator, and the state of every of it is control bits.
– Once the Timer stops incrementing, note the final value of timer T4:1’s accumulator, preset, and the state of it is control bits below:
Final State (Switch I:1/0=Closed):
T4:1.ACC = _____ T4:1.PRE = ______ T4:1/EN = ____ T4:1/TT = ____ T4:1/DN = ____

– Toggle the state of switch I:1/0 plenty of times, and observe the operation of the Timer in both the DataTable display and within the Ladder Rung program display.
– Confirm that when the rung is taken false, the accumulator and all 3 control bits are reset to zero. One of these timer is a non-retentive instruction, in that the reality of the rung could cause the accumulator and control bits to be reset (=0).
Conclusions:
Use the TON instruction to show an output on or off after the timer has been on for a preset time interval. This output instruction begins timing when its rung goes “true”. It waits the specified amount of time (as set within the PREset), keeps track of the accumulated intervals which have occurred (ACCumulator), and sets the DN (done) bit when the ACC (accumulated) time equals the PRESET time.

As long as rung conditions remain true, the timer adjusts its accumulated value (ACC) each evaluation until it reaches the preset value (PRE). The accumulated value is reset when rung conditions go false, no matter whether the timer has timed out.

Cascaded TON Timers

– Insert a brand new rung containing a second timer just below the first rung as shown below. This second timer T4:2 will likely be enabled when the first timer’s Done bit T4:1/DN goes true or high (1).

– Upon getting completed this addition to your program, download your program to the PLC and select RUN.
– Toggle the state of switch I:1/0 to ON and observe the operation of the timers in your program.
– Bring the DataTable display into view, and pay particular attention to the way in which through which the timers are cascaded (one timer starts the subsequent).
– Try changing the value of one of many timer presets by double clicking on the preset value within the DataTable display, after which entering a new value.
– Run the timers through their timing sequence quite a few times. Do not move on until you’re satisfied that the timers are working as you’d expect
On this exercise now we have utilized just two timers, but there may be nothing stopping us from sequencing as many timers as we wish. The one thing to remember is; to make use of the DN (done) bit of the previous timer to enable the subsequent timer in the sequence. Obviously locating the timers on consecutive rungs, and employing consecutive numbering will make such a program much easier to read and trouble-shoot.

Self Resetting Timers

– Place the PLC into the PGM mode, and modify the first rung of your program as depicted below.

– Upon getting modified your program, download it to the PLC and place the PLC into the RUN mode.
– Close switch I:1/0 and observe the operation of the timers. The timers should now be operating in a continuous loop with Timer1 starting Timer2, after which when Timer2 is done, Timer1 is reset by Timer2’s done bit. As before, when Timer1 is reset, it in turn resets Timer2 which causes Timer2’s done to go low (T4:2/DN=0). Once Timer2’s done bit is low, the sequence is back to where it originally began, and the timing sequence will start over once again on the very next scan.
– Remove the primary instruction (switch XIC I:1/0) from rung zero of your program.
– Download and RUN this modified version of your program
– Does the timing operation continuously sequence as before? It should!
– Can you stop the timing sequence? Not without taking the PLC out of the RUN mode! In many applications there may never be a have to stop such a timing sequence, so a switch won’t be used or needed.
On this exercise we cascaded two timers, but as before there is nothing to stop us from cascading as many timers as we wish. The thing to recollect here is; utilize the DN (XIC or “NOT”done) bit of the last timer in the sequence to reset the first timer in the sequence. Once again, consecutive rungs, and numbering will make a program much easier to read and trouble-shoot.

The TOF Timer …. (Timer OFF Delay)

In Allen Bradley PLC programming, the TON timer is by far the mostly used type of timer. Most individuals consider TON timers to be simple to make use of and understand. In comparison, many individuals find the operation of the Allen Bradley TOF (Timer OFF delay) timer to be less intuitive, but I will let you decide for yourself.

Make it possible for switch I:1/0 is Closed, and then enter or modify your existing program to match the one shown below.

– Once you have your program entered, and have ensured that it’s correct, download it to the PLC.
– Make sure that Switch I:1/0 is Closed, after which place the PLC into the Run mode.
– Right click on the Timer instruction, and select “GoTo DataTable” from the drop-down menu.
– Note the initial value of timer T4:1’s accumulator and preset in the spaces below. Also indicate the state of each of the timer’s control bits within the spaces provided:
Initial State (Switch I:1/0=Closed):
T4:1.ACC = _____ T4:1.PRE = ______ T4:1/EN = ____ T4:1/TT = ____ T4:1/DN = ____

– Open switch I:1/0, and punctiliously observe the incrementing of the timer’s accumulator, and the state of each of it’s control bits.
– Once the Timer stops incrementing, note the ultimate value of timer T4:1’s accumulator, preset, and the state of it is control bits below:
Final State (Switch I:1/0=Open):
T4:1.ACC = _____ T4:1.PRE = ______ T4:1/EN = ____ T4:1/TT = ____ T4:1/DN = ____

– Toggle the state of switch I:1/0 quite a few times, and observe the operation of the Timer in both the DataTable display and within the Ladder Rung program display.
– Confirm that when the rung is taken true, the accumulator and all 3 control bits are reset to zero. The TOF timer like the TON timer can also be a non-retentive instruction and might be reset by changing the reality of the rung.
Conclusions:
Use the TOF instruction to turn an output on or off after its rung has been off for a preset time interval. This output instruction begins timing when its rung goes “false.” It waits the specified amount of time (as set within the PRESET), keeps track of the accumulated intervals which have occurred (ACCUM), and resets the DN (done) bit when the ACCUM (accumulated) time equals the PRESET time.

The Accumulated value is reset when rung conditions go true regardless of whether the timer has timed out.

The RTO Timer …. (Retentive Timer ON)

– Be sure that switch I:1/0 is Open, and then replace the TOF timer in your program with a RTO retentive timer.
– Now insert a brand new rung below the timer, and add the XIC,I:1/1 and RES,T4:1 instructions.
– Your program should now match the one shown below:

– After getting your program entered, and have ensured that it’s correct, download it to the PLC.
– Make sure that both Switches are Open, and then place the PLC into the Run mode.
– Right click on the Timer instruction, and select “GoTo DataTable” from the drop-down menu.
– Note the initial value of timer T4:1’s accumulator, preset and control bits. Are we starting off with the same values we had within the TON exercise? Try to be answering Yes.!

– Close switch I:1/0 for 2 or 3 seconds after which Open it again.
– Note that the timer stopped timing when the rung went false, however the accumulator was not reset to zero.
– Close the switch again and leave it closed which will allow the timer to time-out (ACC=PRE).
– Once timed out, note the state of the control bits
– Open the switch, and once again note the state of the control bits.

– Now close Switch I:1/1 and leave it closed. This may cause the Reset instruction to go true.
– Close switch I:1/0 momentarily to see if the timer will start timing again. It shouldn’t!
– Open Switch I:1/1 which is able to cause the Reset instruction return to false.
– Now toggle switch I:1/0 several times and note that the timer should again start timing as expected.

– Repeat the foregoing steps, until you’re satisfied that you clearly understand the operation of both the RTO timer, and the Reset instruction.
Conclusions:
An RTO timer functions the identical as a TON with the exception that after it has begun timing, it holds its count of time even when the rung goes false, a fault occurs, the mode changes from RUN to PGM, or power is lost. When rung continuity returns (rung goes true again), the RTO begins timing from the accumulated time which was held when rung continuity was lost. By retaining its accumulated value, retentive timers measure the cumulative period during which rung conditions are true.

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